Beta-Adrenergic receptors are present in HeLa cells and the number of these receptors can be increased by culturing the cells in the presence of butyrate. At low concentrations of butyrate, receptor number is increased and at higher concentrations, both number and ability to activate adenylate cyclase are enhanced. Astrocytoma cells also contain beta-adrenergic receptors which are permanently coupled to adenylate cyclase. The beta-adrenergic receptor in HeLa can also directly enhance phospholipid methylation, and this effect is not mediated by activation of adenylate cyclase. The amount of phosphatidylcholine in the receptor's microenvironment affects the apparent number of beta-adrenergic receptors and the ability to activate adneylate cyclase. Prior exposure of cells to l-isoproterenol causes the cells to become refractory to a second stimulation (desensitized). Additionally, the apparent number of Beta-receptors decreased. Inhibitors of phospholipase A2 block desensitization and activators can cause desensitization in the absence of agonist.